Tranquility

Well, based on Rich's numbers, I am going to resign myself to the underperformance of this system. In looking at all parts of the unit, I also noted that the foam insulation in the bubble box is degraded, which would also increase heat load. I hope this insulation isn't falling on the upper side of the evaporator as it is difficult to access. The airflow at the vents is good, but I can't be sure all of the air is flowing over the evaporator. Thank you all for your ideas and suggestions. Brian

Thanks for the replies. I had some time to work with the system yesterday and using your advice, here is what was done. In researching the dash unit, I found the unit components have A-R-A labels on them and while I could not find information on this company, the components look identical to the Acme bubble AC units. (Anybody know what the proper R12 charge weight was in these units with 40' hose?) The TXV is externally balanced and I like the idea of installing a tee to check evaporator outlet pressure. (Thanks Fred) It will take some time to get that done however as I don't have all the hardware. The system pressures do slowly equalize when the compressor is de-energized. Double checking the condenser fan cooling, I found a short cycling circuit breaker for the condenser fan which was replaced. One terminal of the CB had become hot due to resistance and slightly melted the terminal. The condenser fan is controlled by a triad pressure switch on the HP line just after the drier which controls a fan relay. This relay can be easily bypassed to run the condenser fan continuously while charging, which is what I did. , I reclaimed the refrigerant and opened the system. High pressure, high volume air flowed freely from the compressor at the DP to the TXV inlet, so I do not suspect problems with the HP hose, front frame mounted condenser, drier or hoses to TXV. I also checked the inlet and outlet of the TXV for debris and none was noted. Sealed the system back up and pulled extended vacuum for 1.5 hrs. I recharged the system until the drier sightglass showed some bubbles and the evaporator outlet fluctuated between 30-38 F, with slight frost/condensation on the first part of the return hose. The unit still performs poorly in my opinion, or is just severely undersized. Using a Fluke thermal gun, I was able to obtain the following: there was 10F subcooling across the condenser, the evaporator outlet temperature hovered in the 30's, but a scan of the coils revealed they were only in the low 60's. This was close to the vent outlet temperatures. The compressor pressures on a 73F morning were 200 high/15 low, again taken at the compressor. I am now researching the evaporator size and configuration. I have read that some evaporators which split the refrigerant into capillary tubes after the TXV have a 1 bar (14psi) pressure drop. Still reading more on this, so I might be wrong. Just pure speculation, but if there is some blockage of the capillary tubes in the evaporator, would that explain the lower outlet pressure without the coils cooling effectively??? My thinking is that if some blockage is present, the overall tonnage rating of the evaporator would be less. What cooling does take place would be dispersed thruout the fins which act as a heat exchanger, but the dimenished capacity would allow exit temperature to read in the 30's. Any thoughts on this idea? If the evaporator does need replacing, it will have to wait due to the ease of access and travel plan dates approaching. Brian Campbell

Hi everyone. First post as I have followed these threads and now have a problem I can't resolve. Forgive the rather long post, but I am trying to provide all the details. Skip on if you have not interest in AC systems. My situation is: I have a 1986 Beaver Marquis Garnet 40' motorhome with Cat 3208 diesel pusher. I am having a problem with the in dash air conditioner. The system had lost R12 freon charge before I purchased it and I have subsequently opened, flushed thoroughly, installed new R134a o-rings and dryer, pulled extended vacuum, drained compressor and introduced 8oz PEG oil with UV dye and attempted to recharge the system with R134a. The gauges hook up on the rear of the Sanden compressor and have back seating valves which were opened midway. I reused the old R12 condensor. My initial problem was that I was getting low low pressure as the high pressure climbed. I subsequently changed the thermal expansion valve when the warming of the bulb had no effect on low side pressure. Vent temperatures were almost ambient. Thinking the THX was bad, I had to find a replacement based on physical characteristics as there were no markings on the THX head or body. I don't remember the specifications for the replacement, but tend to recall 2 ton rated. Upon trying to charge the system with the new THX installed, I am getting high dash vent temperature (82 ambient with register of 65) and the low side pressure won't go above 15 psig. The high side pressures are in range with the condensor fan running. (82 ambient with high side pressures of 225-240) There is frosting of the evaporator outlet with constant condensation. The THX is externally regulated and the sensor bulb is well attached and insulated. The system is currently overcharged as there are no bubbles in the sight glass with the system in operation. I realize there is some inefficiency of R134a, but this isn't even close. I should have register tempuratures in the 40's. The measured superheat across the condensor was over 10 degrees, but I returned the specialized sensors and don't have accurate numbers. Even so, the top coils of the condensor can't maintain contact with the skin while the lower coils can be held, so vapor to liquid condensing is taking place there. I question whether I installed the correct THX with a replacement of the correct rating. The low side hose didn't show any restrictions during flushing and I can't imagine it collapsing internally with 15 psi inside. I also checked the airbox doors to make sure they were sealing and positioned properly. Short questions: Would the wrong THX cause the low suction side readings? Would the location of the line taps affect the readings this much? While the air coming out the vents is cooler, it isn't cold...any enlightenment appreciated. Brian Campbell